1. Field
Disclosed herein is a method for casting concrete products by means of a substantially horizontal slipforming process, wherein the concrete mass is pressurized by means of one or more feed screws. More precisely, disclosed herein is a method and apparatus for casting a zero-slump concrete mass. The cast products may be hollow-core slabs or solid slabs.
2. Description of Related Art
When casting with traditional extruder and slipformer casting machines, the casting mold is formed by a casting bed and side walls and an upper surface moving along with the casting machine and forming the cross section of the product to be cast to the desired shape and size. When the casting machine proceeds, the side walls and the upper surface, and if necessary, the elements forming one or a plurality of hollow cores to the product to be cast, perform motion compacting the concrete mass. The ready-cast product remains on the casting bed to harden. Because the cast fresh slab remains lying on the casting bed in its final form, a high stiffness is required from the concrete mass to be used in the solutions of prior art.
The stiff concrete mass used in the solutions of prior art causes strong wear of the wear parts of the slipforming machine, like the feed screws and the hollow-core forming elements, whereby these wear parts must be changed relatively often. In connection with the change of the wear parts, also the casting process of the production plant must be interrupted for the duration of the change. The stiff concrete mass also causes mechanical burden on the processing devices, particularly on the structures involved in compaction of the concrete mass, like the troweling devices of the upper surface, side walls and the hollow-core mandrels, and the rotating devices of the screws, and degradation of the compacting efficiency caused by the fast wear. In known solutions, particularly with tall concrete products or with thick layers of concrete, the concrete does not compact uniformly throughout, causing unwanted variations in the quality of the end product.
The slipforming technique for manufacturing hollow-core slabs and massive slabs is well known in the art. For example Patent publication FI 80845 discloses a method and an apparatus for casting a hollow-core slab. The compacting method described therein is based on reciprocal swinging of the hollow-core mandrel simultaneously with the reciprocal longitudinal motion. Nowadays, the heights of the slabs are increasing, whereby also the heights of the hollow cores increase. In case of high hollow cores, with the described swinging of the hollow-core mandrel the adequate compacting of the concrete is not achieved.
In the compacting method described in patent publication FI 110174, a short reciprocal longitudinal motion of the hollow-core mandrels goes along an arch-like trajectory. When using this solution, vertical movement of the mandrels is obstructed by stiff, compacted mass surrounding the mandrels, and the adequate compacting of the concrete is not achieved. The obstruction of vertical movement of the mandrels causes additional burden on the driving devices and premature damages.